Search for copper sulfides and sulfur chemistry in the Martian crust, based on geochemical data returned by NASA's MSL rover

自2012年8月以来，美国宇航局火星科学实验室（MSL）探测器在火星盖尔陨石坑（Gale crater）沿轨道（约18公里）连续探测到铜元素（Cu），但其量化仍然存在问题。根据目前的模型，Cu丰度在大多数地方< 50ppm，但在某些地区可能高于背景值~20倍。该项目的目标是：(a)建立铜定量的实体模型，(b)确定含铜矿物（特别是在铜富集程度高的目标），(c)推断其可能的形成途径。这项研究将重点关注ChemCam传回的数据，但也将使用探测器上的两种仪器APXS，分别利用LIBS（激光诱导击穿光谱）和x射线荧光来推断火星表面物质的化学成分。目标(a)需要详细分析两个ChemCam发射带，其中两个最强的Cu发射线（324.8 nm和327.5 nm）与其他元素（特别是Ti）的发射线重叠。为了实现目标（b-c），将特别关注Cu与Ni、Zn、S以及主要化学元素（Si、Al、Ca、Mg、Na、Ti、K、Mn）的潜在相关性，这些元素的丰度在任务期间每天都要例行测定。升高的Cu可能与硫（硫化物分离？）有关，并将注意证明或反驳这一假设。本研究的高水平目标是：(i)追踪的命运铜在表面和内部的火星表面(尤其是比较丰度与SNC陨石和BSM[大部分硅酸盐火星]),(2)说明火星硫循环的一个特定方面(最重要的地球化学循环在火星表面超过几十亿年)和(3)解决这个问题如果从地球上已知成矿过程可能发生在火星上(可能比地球上小得多的速度和空间尺度)。

The element copper (Cu) is being detected (almost) continuously along the traverse (~18 km, since Aug 2012) of NASA’s MSL rover in Gale crater, Mars, but its quantification remains problematic. According to the current model, Cu abundances are < 50 ppm at most places, but may be ~20 times above background in selected areas. The goals of this project are: (a) develop a solid model of Cu quantification, (b) identify the Cu-hosting minerals (especially at targets with high Cu enrichment) and (c) infer their likely pathways of formation. This study shall focus on data returned by ChemCam, but will also use APXS, - two instruments onboard the rover that utilize LIBS (Laser Induced Breakdown Spectroscopy) and x-ray fluorescence, respectively, to infer chemical composition of Martian surface material. Goal (a) requires detailed analysis of the two ChemCam emission bands where the two strongest Cu emission lines (324.8 & 327.5 nm) overlap with lines of other elements (Ti in particular). In order to achieve goals (b-c) particular attention will be given to potential correlations of Cu with Ni, Zn, S as well as major chemical elements (Si, Al, Ca, Mg, Na, Ti, K, Mn) whose abundances are routinely determined on a daily basis over the mission. Elevated Cu might be correlated with sulfur (sulfide segregation?) and care will be given to prove or disprove that hypothesis. The high-level goals of this study are: (i) track down the fate of Cu at the surface and in the interior of Mars (in particular compare surface abundances to those in SNC meteorites and BSM [Bulk Silicate Mars]), (ii) illustrate a particular aspect of the Martian sulfur cycle (the most important geochemical cycle at the Martian surface over billions of years) and (iii) address the question if ore-forming processes known from Earth might have taken place on Mars (perhaps at much smaller rate and spatial scale than on Earth).